JP2743382B2 - Inverter device for driving induction motor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an inverter device for driving an induction motor, and more particularly to appropriately controlling the power factor of the induction motor,
It concerns protection against overload.

[Conventional technology]

FIG. 5 is a block diagram showing a conventional induction motor driving inverter device disclosed in Japanese Patent Publication No. 61-20236.

In the figure, 10 is a DC power supply, 11 is an inverter section composed of a power transistor, 22 is a current transformer, 13 is a frequency setter, 14 to 21 are pulse width modulation signal generation circuits (hereinafter referred to as PWM generation circuits 99 ), and 23 is Current polarity detectors, 29 and 30 are current level detectors, 24 is a phase difference detector, 26 is an amplifier, 27 is a switch, these constitute an inverter device,
The induction motor 12, which is a load, is driven.

Next, the operation of this conventional example will be described. The DC power supply 10 converted by the converter unit (not shown) receives the frequency command f _R from the frequency setting unit 13 and the signal of the PWM generation circuit 99 based on the voltage correction command from the amplifier 26 to output the inverter unit 1
The power transistor 1 is switched and converted to an AC power supply with an appropriate output frequency and output voltage, and the
Added to 12.

On the other hand, the current polarity detector
The current phase P2 is detected by 23, and is compared with the voltage phase signal P1 from the PWM generation circuit 99 by the phase difference detector 24 to become a phase difference signal, and the amplifier 26 gives a voltage correction command. Further, the output of the current transformer 22 is converted into an absolute value by the output current level detectors 29 and 30. When the output current level reaches a certain value or more, the switch 27 cuts the voltage correction command.

[Problems to be solved by the invention]

Since the conventional inverter for driving an induction motor is configured as described above, even if the load torque increases and the motor current exceeds a certain value, the voltage correction command is cut and the power factor control is suppressed only. Therefore, the protection of the induction motor and the protection of the switching element such as the power transistor of the inverter device are not required, but another protection circuit (for stall control) is required.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances. In a steady state, the induction motor can be operated at an appropriate power factor, and the output frequency is limited with respect to an excessive load torque, thereby switching the induction motor or the inverter device. It is an object of the present invention to provide an induction motor driving inverter device that protects elements from overcurrent and can stably operate the induction motor.

[Means for solving the problem]

An inverter device for driving an induction motor according to the present invention includes:
An inverter device which converts an AC power supply into a DC power supply once, converts the DC power supply into an AC power supply having an arbitrary output frequency and output voltage, and supplies the AC power to the induction motor. Output voltage correction means for adjusting the output voltage by adjusting the voltage correction parameter according to the magnitude of the phase difference and the reference value, and detecting an excessive load when the voltage correction parameter of the output voltage correction means exceeds a reference by a predetermined value or more. And output frequency control means for limiting the output frequency.

[Action]

With the above-described configuration, the power factor of the load induction motor is appropriately controlled, and the output frequency is limited with respect to excessive load torque.

〔Example〕

 The present invention will be described with reference to examples.

FIG. 1 is a book diagram of an embodiment of the present invention for controlling the output frequency of an inverter device according to the absolute value of a current to an induction motor, and FIG. 2 is a flowchart showing the operation of the embodiment. It is.

In FIG. 1, reference numeral 10 denotes a DC power supply obtained by converting an AC power supply to DC by a converter unit (not shown), and 11 denotes an inverter unit comprising a power transistor for converting the DC power supply to an arbitrary output frequency and output voltage. , 22 is a current transformer for detecting the current of the induction motor 12 of the compressor as a load, 13 is a frequency setting device, 18 is an F / V * converter, 98 is a frequency limiter, 99 is a pulse width modulation signal generation circuit ( Hereafter, a PWM generation circuit), 23 is a current polarity detector, 24 is a phase difference detector, 26 is an amplifier, 29 and 30 are current level detectors, and these constitute an inverter device for driving an induction motor.

Next, the operation of the inverter device will be described. DC power supply 10 converted by a converter unit (not shown)
Is PW by the frequency command f from the frequency setting device 13 through the frequency limiter 98 and the voltage correction command V from the amplifier 26.
The power transistor of the inverter section 11 is switched by the signal of the M generation circuit 99 , converted into an AC power supply having an appropriate output frequency and output voltage, and supplied to the induction motor 12.

On the other hand, the current polarity detector
The current phase P2 is detected by 23 and is compared with the voltage phase signal P1 from the PWM generation circuit 99 by the phase difference detector 24 to become the phase difference signal φ.
Becomes

Further, the output of the current transformer 22 is converted into an absolute value by the current level detectors 29 and 30. When the output becomes a certain value or more, the frequency limiter 98 limits the frequency command f to the PWM generation circuit 99 .

In this way, in the steady state, the induction motor is operated at an appropriate power factor (for example, a power factor at which the induction motor operates at a high efficiency), and the load torque is reduced as in the induction motor of the compressor of the room air conditioner. That is, when the output torque is almost proportional to the output frequency, the excessive load torque
The output frequency of the inverter is detected by the absolute value of the output of the inverter 22, and the output frequency of the inverter is limited, and the rotation speed of the induction motor is limited and suppressed.

Therefore, the induction motor 12 and the power transistor of the inverter unit 11 are not damaged by overcurrent due to excessive load torque, and the induction motor can stably operate without stalling due to excessive load torque.

Although the above embodiment has been described with a hardware configuration, the same effect can be obtained by using a microcomputer program.

Next, the operation of the above embodiment will be described with reference to the flowchart of FIG.

When starting (100), first, the magnitude of the current value of the induction motor is determined (101). If the current is larger than the reference value, the frequency is lowered (102). (103) If it is smaller than the reference value, the frequency is allowed to rise (103). Next, the phase difference between the voltage and current of the induction motor, that is, the magnitude of the power factor is determined (105).
If the power factor is too low below the reference value, the voltage correction parameter is lowered (106), and if it is too high, the voltage correction parameter is raised (107). The actual output voltage is determined by V obtained by multiplying the reference voltage V * determined by the frequency setting device 13 and the above-described voltage correction parameter.

Next, another embodiment of the present invention for controlling the output frequency of the inverter device according to the voltage correction parameter of the output voltage correction means will be described.

FIG. 3 is a block diagram of the embodiment, and FIG. 4 is a flowchart showing the operation of the embodiment.

In FIG. 3, the same reference numerals as those in FIG. 1 denote the same or corresponding parts, and a description thereof will not be repeated.

 96 is a voltage corrector, and 97 is a phase difference determiner.

Next, the operation of this embodiment will be described. The DC power supply 10 converted by the converter unit (not shown) receives a frequency command f from the frequency setting unit 13 passing through the frequency limiter 98 and a PWM command V based on the voltage command V via the voltage compensator 96.
The power transistor of the inverter section 11 is switched by the signal of the generation circuit 99 , converted into an AC power supply having an appropriate output frequency and output voltage, and supplied to the induction motor 12.

On the other hand, the current polarity detector
23, the current phase P2 is detected, the voltage phase signal P1 from the PWM generation circuit 99 is compared with the phase difference signal 24 by the phase difference detector 24, and the voltage difference is compared with the reference phase difference φ * by the phase difference determination unit 97. A corrector 96 is added. The voltage corrector 96 corrects the output voltage by adjusting the voltage correction parameter according to the magnitude of the reference phase difference and the detected phase difference, and appropriately controls the power factor.

Here, when the load torque increases, that is, when the motor current increases, the power factor increases and the voltage correction parameter Pa increases, and the frequency limiter 98 suppresses the increase in frequency. The parameter Pa further increases, and the frequency is reduced by the frequency limiter 98.

In this way, in the steady state, the induction motor is operated with an appropriate power factor, and when the load torque is almost proportional to the rotation speed, that is, the output frequency, as in the induction motor of the compressor of a room air conditioner, the excessive load torque is The output voltage is detected by the voltage correction parameter of the output voltage correction device, the output frequency is limited, and the rotation speed of the induction motor is limited and suppressed.

Therefore, even in this embodiment, the induction motor 12 and the power transistor of the inverter unit 11 are not damaged by the overcurrent due to the excessive load torque, and the operation can be stably continued without the stall of the induction motor due to the excessive load torque. .

Although the above embodiment has been described with a hardware configuration, the same effect can be obtained by using a microcomputer program.

Next, the operation of the second embodiment will be described with reference to the flowchart of FIG. When starting (100), first, the phase difference of the voltage and current of the induction motor, that is, the power factor is detected (10).
1) The magnitude of the detected value of the power factor and the reference value are discriminated (102). If the detected value is smaller than the reference value, the voltage correction parameter is lowered (103). If the detected value is too large, the voltage correction parameter is raised ( 104). Next, the voltage correction parameter is applied to a limiter (105), and the output voltage of the inverter device is determined by the voltage V obtained by multiplying the voltage reference V * determined by the frequency setting unit 13 and the above-described voltage correction parameter.

Further, it is determined how much the voltage correction parameter is over the reference (107), for example, + 10%
If it is below, increase of output frequency is permitted (108) and 10%
If the output frequency is in the range of 20% to 20%, the increase of the output frequency is prohibited (109), and if it is 20% or more, the output frequency is forcibly reduced (110).

〔The invention's effect〕

As described above, according to the present invention, there is provided an inverter device for temporarily converting an AC power supply to a DC power supply, converting the DC power supply to an AC power supply having an arbitrary output frequency and an output voltage, and supplying the AC power supply to the induction motor. An output voltage correcting means for correcting the output voltage according to a phase difference between a voltage and a current supplied to the induction motor, and detecting an excessive load according to a voltage correction degree of the output voltage correcting means to control the output frequency. Output frequency control means for controlling the output frequency according to the voltage correction parameter of the inverter device,
A switching element such as a power transistor of an induction motor or an inverter device is protected from overcurrent, and the induction motor can be operated stably without stalling. Further, since the information necessary for the overload control is obtained from the voltage correction degree (voltage correction parameter) at the time of the high-efficiency control, the effect that the configuration is simplified can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of an inverter for driving an induction motor according to one embodiment of the present invention, FIG. 2 is a flowchart showing the operation of the embodiment, and FIG. 3 is a block diagram of another embodiment of the present invention. FIG. 4 is a flowchart showing the operation of the embodiment of FIG. 3, and FIG. 5 is a block diagram of a conventional example. In the figure, 10 is a DC power supply, 11 is an inverter unit composed of a power transistor, 12 is an induction motor of a compressor, 24 is a phase difference detector, 26 is an amplifier, 29 and 30 are current level detectors, 9
8 is a frequency limiter, 99 is a PWM generation circuit, and the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] An inverter device for temporarily converting an AC power supply into a DC power supply, converting the DC power supply into an AC power supply having an arbitrary output frequency and output voltage, and supplying the AC power supply to the induction motor. An output voltage correction means for correcting the output voltage by adjusting a voltage correction parameter according to a magnitude of a phase difference between a voltage and a current and a reference value, and a case where a voltage correction parameter of the output voltage correction means exceeds a reference by a predetermined value or more. And an output frequency control means for detecting an excessive load and limiting the output frequency.